In recent years, there is a very strong demand for improvement in performance particularly in the field of a rotating machine, a medium or small size transformer, etc. For this reason, as described in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 54-76422, 55-82732 and 57-203718, in order to bring out magnetic properties of a non-oriented electromagnetic steel sheet as much as possible, a method wherein the stress relief annealing for removing stamping stress of a non-oriented electromagnetic steel sheet in the production of an iron core is utilized to simultaneously conduct the recrystallization and crystal grain growth of the steel sheet, thereby improving magnetic properties to attain substantially the same effect as that attained when use is made of a non-oriented electromagnetic steel sheet of higher grade, has widely been used in the art. For this purpose, a box or tunnel furnace wherein electricity or gas is used as a heating source has been generally used because the stress relief annealing should usually be conducted under conditions of a temperature in the range of from 700.degree. to 850.degree. C. and a soaking time of one hour or longer.
In the above-described conventional stress relief annealing method, however, the annealing including heating, soaking and cooling requires several hours or longer. Further, since the annealing is a batch process independent of a series of iron core manufacturing steps, it leads to an increase in the time necessary for the manufacturing process and an increase in the complexity of the manufacturing process, so that productivity is very poor.
In view of the above, an object of the present invention is to provide a process for producing a non-oriented electromagnetic steel sheet having excellent magnetic properties after stress relief annealing which can sufficiently attain an improvement in the desired magnetic properties even in stress relief annealing for a short period of time and improve productivity through a reduction in the time necessary for the manufacturing process and a simplification of the manufacturing process.